Its goal is to help people securing their web applications against attacks like SQL Injections, Cross Site Scripting, Cross Site Request Forgery, Local & Remote file inclusions.

The difference with most WAF (Web Application Firewalls) out there is that it does not rely upon signatures to detect and block attacks. It uses a simpler model where, instead of trying to detect "known" attacks, it detects unexpected characters in the HTTP requests/arguments.

Each kind of unusual character will increase the score of the request. If the request reaches a score considered "too high", the request will be denied, and the user will be redirected to a "forbidden" page. Yes, it works somewhat like a spam system.